using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using ReactiveETL.Operations;

namespace ReactiveETL.Activators
{
    /// <summary>
    /// Join activator for an operation. The first time the activator is iterated will trigger the operation pipeline.
    /// </summary>
    public class OperationJoinActivator : JoinActivator<Row>, IEnumerable<Row>
    {
        /// <summary>
        /// Joined operation
        /// </summary>
        public IObservableOperation Operation { get; set; }

        private RecordOperation _recorded;

        private void CheckOperation()
        {
            if (_recorded == null)
            {
                // To save memory, if the last operation is a record, we do not create a new one.
                if (Operation is RecordOperation)
                {
                    _recorded = (RecordOperation)Operation;
                }
                else
                {
                    _recorded = Operation.Record();
                }
                _recorded.Start();
            }
        }

        #region IEnumerable<T> Members
        /// <summary>
        /// Returns an enumerator that iterates through the collection.
        /// </summary>
        /// <returns>
        /// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.
        /// </returns>
        /// <filterpriority>1</filterpriority>
        public override IEnumerator<Row> GetEnumerator()
        {
            CheckOperation();
            return _recorded.Result.GetEnumerator();
        }

        #endregion

        #region IEnumerable Members

        /// <summary>
        /// Returns an enumerator that iterates through a collection.
        /// </summary>
        /// <returns>
        /// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
        /// </returns>
        /// <filterpriority>2</filterpriority>
        IEnumerator IEnumerable.GetEnumerator()
        {
            CheckOperation();
            return _recorded.Result.GetEnumerator();
        }
        #endregion
    }
}
